In off-shore oil industry, chemical tanks are commonly used for receiving, storage, back-loading, processing and transport of various fluids such as helifuel, Mono Ethylene Glycol (MEG), hydrocarbon contaminated drilling and completion fluids and crude/waste oil. Present tanks are provided as separate units arranged on various locations onboard an offshore installation. For example, on a semi-submersible drilling rig the location is typically the main deck, riser/pipe deck. Normally 2″ rubber hoses are connected manually for transferring liquid to and from tanks, dependent upon operations.
Mounting and arranging prior art chemical tanks offshore is time consuming and also commonly requires welding of boundaries to obtain a drip/spill tray to capture any leakage from the tanks.
In for instance well test and completion operations the mounting/arranging is especially time consuming in connection with the installation of 30/50 m3 storage tanks. Such installation does not only comprise welding and sea-fastening, including the boundaries mentioned above, but also the rig up of all rubber hoses for inlet and outlet, as well as for vent lines towards safe routing overboard, or to a flare system.
Due to limitations on rig structure, spreader beams are needed to be spotted and welded to strengthen the deck to distribute the heavy load from theses storage tanks mentioned above.
A further disadvantage of present 30/50 m3 storage tanks is that they have to be shipped empty. Dimensions on some of the storage tanks are wider (width and height) than allowable for transport onshore with transport trucks. With a frame being wider than 2.6 m, a follow car is needed and transport is only allowed at certain time periods and weekdays.
Further, the 30/50 m3 storage tanks are only for atmospheric pressure, and may not be used for liquids having concentrations of hydrocarbon gases entrapped.
For transportation, liquids from the 30/50 m3 storage tanks must be transferred to portable slop tanks. Common sizes for portable tanks on the marked are 500 gallons and 1000 gallons (i.e. commonly from 2300 liters up to max 4500 liters), and they come in both vertical and horizontal configurations.
These portable tanks have only atmospheric pressure rating, and needs to be manned during filling operations. The filling occurs through an open manhole at the top of the tank. Consequently, personnel are exposed to fumes from hydrocarbon contaminated waste during filling. Further, the portable tanks are open vented under filling, and explosive fumes are a potential hazard onboard. The mix of both vertical and horizontal portable tanks shipped offshore, in combination with the deck layout (I-beams), makes it difficult to spot tanks next to each other for efficient space exploitation onboard a rig, where normally there is very little space available.
In addition to the above-described issues related to present storage tanks and/or portable slop tanks, some rigs also have limitations regarding the filling of portable slop tanks in that transfer and filling is only allowed after a well is shut in.
Further issues related to the present storage and/or portable slop tanks is that it is time consuming to transfer and fill the portable slop tanks during for instance a production testing, and further that none of the tanks have any integrated protection against fire. In present solutions, water must be rigged up/directed if not present onboard.
One or more embodiments of the present invention may avoid or alleviate at least some of the disadvantages of the prior art tanks and/or tank systems.